In the automotive industry, wire bundles must often be passed through apertures in a bulkhead panel of a vehicle as it is being wired. A grommet assembly is desirable to support the wire bundle and protect it from the sharp edges of the aperture. As electronic components have increased in number and complexity, it has become necessary to protect and support much larger and heavier wire bundles. Consequently, the trend is toward grommet assemblies, often known as hardshell grommet assemblies, that are larger and capable of handling and accurately locating the larger wire bundles. These hardshell grommet assemblies generally include a grommet body with a passage through which the wire bundle extends. Often, these hardshell grommet assemblies also provide for injecting a sealant material into the passage around the wire bundle. This sealant, sometimes in conjunction with wire clips inside the passage, holds the wire bundle fast with respect to the grommet body. Some means is necessary to attach the grommet body to the bulkhead panel overlying the aperture as the vehicle is being wired. Various means for doing so are disclosed in patents assigned to the assignee of the present invention. U.S. Pat. No. 4,289,924 to Pearce et al. shows a hardshell grommet assembly 10 that is attached to a bulkhead panel 14 overlying an aperture 12 by bolts or other fasteners that pass through holes in the bulkhead panel 14. A grommet assembly that requires no fasteners passing through the bulkhead panel is disclosed in U.S. Pat. No. 4,407,042 to Schramme et al. There, a grommet assembly 10 has a shank 38 that is inserted through the bulkhead panel aperture. Then, a U-shaped retainer 22 is pushed in from the side into tapered slots 54 in the shank 38 to attach and retain the grommet assembly 10. Both of these attachment methods work well, and have been extensively used. However, both require that some part of the structure of the grommet body itself be directly used to attach the grommet body. A retainer for a grommet body that was structurally independent of the grommet body, and which could, therefore, be universally used with any grommet body of the type described, would be desirable.